Thread Repost -- Carburetor Synchronization using Twinmax

[TheImp]

Hey guys, I posted this thread yesterday in the maintenance section but it seems to not be too frequently visited as this section so I want to repost this thread here hoping that it won't be missed by someone who can explain a few things to me. If this crosspost is breaking the rules I apologize, I'll delete the original.
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For those of you familiar with the twinmax used to sync a bikes carbs I have some questions before I start on my initial maintenance next week.

The zeroing of the device is self explanatory but there is one part:

Adjust the idle/slow running screw on the carb being adjusted (not the reference carb) until the meter shows an equal deviation on each size of zero. The meter is very sensitive, so care must be taken to use small increments of adjustment. Blip the throttle each time you make an adjustment to ensure the throttles are properly seated.

The carbs on my bike (vulcan 500) appears to have only one adjustment screw to sync the carbs and not one per carb. So I assume I just turn that one screw either clockwise/counterclockwise until the needle on the twinmax shows zero, right? What is kind of confusing for me is the fact that with one screw, it must only be adjusting one of those carbs and perhaps the other is a reference cylinder that is a constant baseline, is that right or am I wrong in my logic?

The next part is more confusing:

Now adjust the carb throttle actuator-this is either a cable or screw acting onto a plate or rod and may be hidden inside the carburetor top. Be careful to make only small adjustments. Note that if there are locking nuts on the adjusters, doing these up will affect the setting so double check the results and blip the throttle to settle things out.

According to my manual this bike has an accelerator and decelerator cable that goes to the carbs. Does this instruction mean that I should adjust the accelerator cable at the throttle body? Ok, so if I adjust this one accelerator cable it certainly isn't controlling both sides of the carbs, but perhaps just one side and the other is some sort of constant that I have to match? Because if that cable directly controlled both sides of the carb then adjusting it would seem to make no difference in balancing it. I also imagine the decelerator cable has nothing to do with this procedure.

If anyone can offer their knowledge I would greatly appreciate it since I'm just starting out with maintenance. Thanks!

One other thing is that my service manual has instructions only for balancing the carbs at idle with the one butterfly screw but mentions nothing about balancing the carbs with an open throttle. Should that mean anything to me or is the balancing at open throttle important regardless?

EDIT: Deleted original thread in other forum.

[paul246]

I use the Twin-Max on my Valkyrie (6 carbs) and it works great.

On the Valkyrie, #3 carb is not adjustable, it is factory set and used as the baseline carb by which the others are balanced. This would be the same for the Vulcan with 2 carbs, the non-adjustable carb is your reference carb.

The only adjustment I have ever done is the air volume screw. I have never adjusted anything else other than idle set which on the Valkyrie is one simple knob that adjusts all six carbs at the same time. In my case the tolerances were all good, but that is what you would have to check for when you are getting ready to sync your carbs.

You could have someone else slowly rotate the throttle (engine off) to make sure each carb is matched as far as external linkage goes. If not, make the adjustments and then sync the carbs.

I sync my carbs at idle, then open the throttle up a bit and let go and watch to make sure everything settles back into sync.

Place a box fan to blow over your engine while doing this job as heat will be generated and some airflow is required to help the cooling system remove it. Especially important when doing an air-cooled engine.

[TheImp]

hi paul246, I appreciate your reply.

You could have someone else slowly rotate the throttle (engine off) to make sure each carb is matched as far as external linkage goes. If not, make the adjustments and then sync the carbs.

Would this require opening the top to view the butterfly valves? In my case since its a single accelerator cable I was confused on how or why I'd need to mess with it. What I mean is with a single throttle cable I am assuming that it will control both carbs at once and IF that were the case then I am thinking that making adjustments using the throttle cable is not necessary because making adjustments to that cable will end up changing both carbs at the same time. Incorrect logic?

My service manual's section on vacuum synchronization only has instructions while the engine is at idle and nothing with opening the throttle and taking measurements. Perhaps thats my clue that synching on a throttle pull isn't needed. Its the twinmax "one size fits all" instructions that threw me a curve ball. Again if there are any mechanics here that can at least validate or invalidate what I said with respect to checking vacuum at throttle please do so.

[paul246]

No, you shouldn't have to open anything on the carbs. Your one throttle cable is most likely connected to something that will actuate both carbs at the same time, thats all. Only if something there is out of whack do you need to make any adjustments, otherwise leave things alone and just do the sync with the volume screw. (wish I had the instructions in front of me). Syncing is a very simple job, it takes me less tha 1/2 hour to do the Valkyrie. Blipping the throttle is done just to raise RPM so that you can check (with Twin-Max) that everything has settled down equally again, if not, just tweak it a bit again and repeat.

[TheImp]

Thanks for the help I think it clarifies a lot for me. I'm trying to wrench without the experience of anyone with me, so I'm inclined to ask crazy questions here.

Thanks again.